The present invention is concerned with indicators of position which indicate the location of a device as a non-continuous quantity by making use of the capacitance. By means of the device, it is possible to indicate the magnitude of a shifting or the position of the device at the desired precision, which precision is selected in advance when the device is manufactured. The solution is particularly favourable when, out of some reason, it is expressly undesirable to pass conductors to the mobile part of the device and when it is also undesirable to use solutions otherwise known, e.g. optical solutions.
A number of different devices have been developed by means of which the shifting of a certain part mechanically can be converted into a quantity expressing the position, which quantity is usually desired as an electrical quantity. Devices of this type can be implemented by making use of different phenomena, e.g. as resistive, inductive, capacitive, optical, etc. As a rule, a common feature of these solutions is the use of an appropriate raster-type image, which is, by making use of the phenomenon mentioned above, converted so as to express the location or movement of a mobile device. The form of this raster is coded in an appropriate way, and even several different means are in themselves known for performing this coding, e.g. Gray code, BCD code, or any other, equivalent. The density of the code determines the precision with which the position or movement is then expressed.
When an optical code reading is used, the medium must, of course, be suitable for the passage of the optical beam of light. On the other hand, it is easy to achieve the desired precision. Instead, when a resistive or inductive indication is used, it is clearly more demanding to achieve the desired precision, as was already stated above. Likewise, in the resistive case, direct contact with the mobile part is usually necessary.
Now it has been noticed according to the present invention that, when the capacitive principle of expression is used, highly remarkable precision and essential independence from environmental circumstances can be achieved by proceeding in the way more closely defined in claim 1. In the other attached patent claims, particular embodiments of the case of the attached claim 1 are defined.